L-lysine is used in the animal feed, human drug and cosmetic industries, and is produced by fermentation using a microorganism of the genus Corynebacterium or the genus Escherichia. In recent years, studies on the development of highly efficient production strains and fermentation process techniques have been conducted.
Many studies have been conducted to control foaming during fermentation of yeasts which are used in beer and wine production, and in recent studies, genes (AWA1, FPG1, and CFG1) having an effect on foaming have been identified (Shimoi H. et al., 2002, Appl. Environ. Microbiol. 68:2018-25; Blasco L. et al., Yeast. 2011, 28:437-51; Blasco L. et al., J. Agric. Food Chem. 2012, 60:10796-07). Herein, it was found that, in the case of a strain with these genes inactivated, foaming significantly decreased compared to that in the case of a parent strain, whereas in the case of a strain that overexpress these genes, foaming increased.
Foaming during culture of yeast occurs through a series of processes as follows. First, mannoprotein mixes with fine gas bubbles generated during fermentation. At this time, the inside of the gas bubbles becomes hydrophobic, and the outside of the gas bubbles becomes hydrophilic. For this reason, the viscosity of the culture medium is increased so that not only various proteins, but also cells mix, resulting in foaming (Swart C W. et al., FEMS Yeast Res. 2012, 12:867-69).
In beer production using yeast, a suitable level of foaming is required, but in fermentation of microorganisms that are used to produce large amounts of useful products such as amino acids, the inhibition of foaming is required. If an excessively large amount of foam is generated during culture, the viscosity of the culture medium will be increased, and thus the oxygen transfer rate (OTR) in the culture medium will decrease, and in severe cases, lysis of the cells will occur. The use of a large amount of an anti-foaming agent for inhibiting foaming can increase production costs in industrial terms and can have an adverse effect on cell growth.
Accordingly, the present inventors have screened genes of a microorganism of the genus Corynebacterium, which have an effect on a large amount of foaming, and have found that, when such genes are inactivated, foaming is effectively controlled so that an ability to produce L-lysine of the strain is increased, thereby completing the present disclosure.